Toe in with radials

[Bob Purton]

Whilst at Jeans with the Isetta at the weekend someone suggested that I adjust the tracking toe in to zero when running on Radial tyres. At the moment the toe in is set at about 4mm as I set it for cross plies before switching to Radials. Any observations?

[Big Al]

An interesting point as they do act differently. No idea on reality or values though. Zero sounds a bit brave on an Isetta. But less would suggest less friction, more power and longer tyre life.

[steven mandell]

My answer is a pragmatic one.
First decide on a local hill where it is easy to obtain your powered top speed by rolling down it.
Bring your wrenches for adjusting toe in, and some fore knowledge of how much to turn your adjuster to achieve a one m.m. change in toe.
Start out down the hill with the zero toe setting.  If you can achieve your powered top speed whilst in neutral- so much the better. Note the speed achieved before worry sets in and note if it is due to wanderlust or a tendency to dartiness.  The former implies not enough toe in, whilst the latter implies too much.
If it is hard to discriminate, go by 1m.m. increments at first, and end up using the least amount of toe in needed to achieve best directional control and least alarming characteristics without detracting from top speed maintained/attained depending on the slope of your hill.
Some compromise between speed attained and best feel may be needed- pick your poison.
At least that was the way that this technique worked for me when I set my HMV Freeway toe in setting.  That was when it still had atrocious and dangerous steering and handling due to improperly engineered built in steering control and suspension induced geometries

I would go down my hill, and not glance upon the speedometer until I began to realistically worry about loosing control/ just felt uncomfortable enough not to wish to push my speed further, and also note whether that point was accompanied by more of a wander, or a tendency for the car to more suddenly wig wag, and then adjust my toe in by the tinyest creak of the wrench.

The balance of terrors in my case was achieved at only about 1/100 ths of an inch of toe in.
The Isetta's steering cannot be as flawed, so such a small increment is not likely to be discriminated in your case.

[Big Al]

This is roughly what I did when modifying the Tripe Tech for Nick. In standard suspension the toe in was huge to gain stability, scuffing the tyres and overheating the engine! With the mods I got it to an acceptable value, but it still requires a lot of toe in and remains brown trouser territory over 50 miles an hour.

[Bob Purton]

Thanks guys. I shall have a tinker with it. Although I did laugh when Steven started to talk about
1/100ths , have you not yet played around with Isetta wheel rims? They were not even built to those kind of tolerances. The British ones anyway.

[steven mandell]

I forgot to mention that I first spun the tires over a sharpened chisel that had been pounded into a moderately angled, pre drilled hole in a block of wood.
The scribed line that resulted from contact betwixt the tire and stationary chisel was my source of measuring points.
This helped factor out production asymmetries as well as bent rim effects.
A piece of wood with 90 degree angle pieces approx as far apart as the track dimension of the vehicle were then used to determine the difference between measurements taken at the hypothetically correct 9 o' clock, and 3 o'clock positions.  However, truth be told, the rearward measurement was always taken from something like The 4, or  8 o'clock position due to issues of access.

[Bob Purton]

Thanks Steven. It does make sense to take the measurements from trued up tyres rather than dodgy rims. I will try and remember 9 o'clock to 3 and 4 o'clock till 8. This fits in well with an Englishman's routine as at 3.30pm we all stop for tea and biscuits!   Joking aside, advise appreciated.

[richard]

don't start us all on biscuits again